Subject: TOS overwrite & 1.1 packet classification

From: "Bob Himlin" <[email-masked]>
Date: Fri, 23 Jul 1999 11:04:54 -0700

Does anyone know a reasonable way to go about handling the case where a CM
is instructed to perform both a TOS-overwrite and packet classification
based on TOS?  It would seem to me that it would be a mistake for an
operator to configure a CM to do this, but I still wonder what the correct
value a CM should to look at for classification purposes - the original or
the overwritten value?  I suppose you could say that it depends on the
interface specified in the IP filter rule that points to the TOS overwrite
rule, so if the TOS overwrite happens on an Ethernet inbound interface, for
example, the classification would be based on the overwritten TOS.  In the
same example, if the TOS overwrite happens on the RF outbound interface, the
original TOS should be used.  Does anyone have any different ideas about how
to implement this?

Bob Himlin, TurboNet Communications
15932 Bernardo Center Drive
San Diego, CA 92127
 [email-masked]

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From: "Mike St. Johns" <[email-masked]>
Date: Mon, 26 Jul 1999 11:36:26 -0700

Bob -

Process these things in order.  Write the new TOS, then do a classification 
based on that TOS, if that's the ordering of the filters.   Think of a 
filter set like this:  Rule 10:  all CPE generated multicast packets get 
TOS 3 and continue.  Rule 20: All TOS 3 packets are given 'gold' docsis 
service.  The first  (10  is applied before 20) filter writes a TOS of 3 
into the packet, the second filter assigns the packet to the gold upstream 
service queue.  So to answer your question, look at the overwritten value - 
the filter sets are in one sense a programming language with a program 
counter and memory locations (the packet).  Also - unless the 'continue' 
bit is set in a matching filter, only the first matching filter applies.

Mike